A NIP, or notice of intended prosecution, is a formal warning that the police may prosecute a driver for certain offences such as speeding or careless driving. For most offences it must reach the registered keeper within 14 days.
In one line: A NIP is a police warning that prosecution may follow for an offence like speeding, normally sent within 14 days.
How a NIP works
A NIP is required under the Road Traffic Offenders Act 1988 for offences including speeding, dangerous driving and failing to comply with a traffic signal. It alerts the recipient that a case may proceed and protects their right to be warned promptly.
A NIP usually arrives with a section 172 request asking the keeper to identify the driver at the time. For example, a keeper caught by a speed camera receives a NIP within 14 days, names the driver within 28 days, and then receives a separate conditional offer of a fixed penalty.
Failing to return the driver details on time is itself an offence, often carrying 6 penalty points and a fine, even if the original allegation is later dropped.
NIP vs FPN
A NIP is only a warning that prosecution is possible and asks who was driving; it is not itself a fine. An FPN is the actual fixed penalty offered later, once the driver has been identified.
The 14-day rule applies to the keeper, so a NIP arriving late at the registered address can sometimes be challenged, though delays caused by an out-of-date V5C will not help the recipient.
Primary source: Road Traffic Offenders Act 1988 (legislation.gov.uk)